Processes for the preparation of cyclic ethers

ABSTRACT

A process for preparing cyclic ethers which comprises contacting a carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

This application is a continuation of prior U.S. application Ser. No. 07/585,564 filing date Sep. 20, 1990 now abandoned.

RELATED APPLICATIONS

The following are related, commonly assigned applications, filed on an even date herewith: U.S. Pat. application Ser. No. 07/585,561, pending; U.S. Pat. application Ser. No. 07/585,560, now abandoned; U.S. Pat. application Ser. No. 07/585,455, now U.S. Pat. No. 5,210,322; U.S Pat. application Ser. No. 07/585,563, now pending; U.S. Pat. application Ser. No. 07/585,559, now U.S. Pat. No. 5,191,123; U.S. Pat. application Ser. No. 07/585,456, now pending; U.S. Pat. application Ser. No. 07/585,565, now U.S. Pat. No. 5,194,613; U.S. Pat. application Ser. No. 07/585,555, now U.S. Pat. No. 5,104,987; U.S. Pat. application Ser. No. 07/585,556, now U.S. Pat. No. 5,164,497; all of which are incorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

1. Technical Field

This invention relates to a process for preparing cyclic ethers which comprises contacting a carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

2. Background of the Invention

Decarboxylation, that is, elimination of the --COOH group as CO₂,is a known process. March, J., Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 1968, pp. 435-436, 477-480 and 878-879, describes various decarboxylation reactions. At pages 435-436, it is stated that aromatic acids can be decarboxylated by heating with copper and quinoline. At pages 477-480, it is stated that aliphatic acids which undergo successful decarboxylation have certain functional groups or double or triple bonds in the alpha or beta positions such as malonic acids, alpha-cyano acids, alpha-nitro acids, alpha-aryl acids, alpha-keto acids, alpha-trihalo acids, beta-keto acids, beta,gamma-olefinic acids and the like. At pages 878-879, oxidative decarboxylation is described in which lead tetraacetate cleaves carboxyl groups, replacing them with acetoxy groups, which may be hydrolyzed to hydroxyl groups. It is stated that compounds containing carboxyl groups on adjacent carbons (succinic acid derivatives) can be bisdecarboxylated with lead tetraacetate. It is also stated that compounds containing geminal carboxyl groups (malonic acid derivatives) can be bisdecarboxylated with lead tetraacetate, gem-diacetates (acylals) being produced, which are hydrolyzable to ketones.

Various processes for the production of ethers are known. A method commonly employed for the preparation of ethers is known as the Williamson synthesis. In the Williamson synthesis, an alkyl halide or substituted alkyl halide is reacted with a sodium alkoxide or sodium phenoxide to give the ether product. For the preparation of aryl methyl ethers, methyl sulfate is frequently used instead of methyl halides. The Williamson synthesis involves nucleophilic substitution of an alkoxide ion or phenoxide ion for a halide ion. Aryl halides cannot in general be used because of their low reactivity toward nucleophilic substitution. Disadvantages associated with the Williamson synthesis include the production of a mole of by-product salt for each mole of ether product and the use of certain methylating agents such as methyl chloride and methyl sulfate which have toxicity and handling problems. Also, at page 316 of March, J., supra, it is stated that the Williamson reaction, i.e., RX+OR'⁻ →*ROR', is not successful for tertiary R (because of elimination) and low yields are obtained with secondary R.

Tamura, Y. et al., Synthesis, 1975, 641-642, relates to the preparation of unsymmetrical sulfides by the alkylation of thiols with alkyl carbonates in the presence of sodium ethoxide and ethanol under refluxing conditions.

Enichem Synthesis SpA, Dimethyl Carbonate Product Bulletin, p. 10, discloses the reaction of phenols with dimethyl carbonate in the presence of a basic catalyst such as NaOH, Na₂ CH₃, tertiary amines or heterocyclic nitrogenous compounds to give methylated phenols. Reaction temperatures of at least 140° C. are required. It is stated that the speed of reaction can be accelerated with catalytic quantities of organic and inorganic halides.

Taylor, Roger, Tetrahedron Letters, No. 8, 1975, 593-596, discloses the thermal decomposition of carbonates to ethers utilizing a palladium-charcoal catalyst.

Witt, H. et al., Angew. Chem., 1970, 82, 79, describes the preparation of substituted diphenyl ethers from ortho- and para-substituted diphenyl carbonates in the presence of small amounts of potassium carbonate and at a temperature of 180° C.-260° C.

Tundo, Pietro et al., Ind. Eng. Chem. Res., 1988, 27, 1565-1571, describes the reaction of dialkyl carbonates with phenols, thiophenols and mercaptans under gas-liquid phase-transfer conditions (continuous flow of gaseous reactants over a solid bed supporting a liquid phase-transfer catalyst) to produce the corresponding ethers and thioethers. The solid bed consisted of potassium carbonate coated with 5 weight percent of CARBOWAX® poly(oxyethylene)glycol 6000 for one set of experiments and alpha-alumina pellets coated with 5 weight percent of potassium carbonate and 5 weight percent of CARBOWAX® poly(oxyethylene)glycol 6000 for another set of experiments. Tundo et al. state at page 1568, right hand column, lines 33-42, that the reaction of alcohols with dialkyl carbonates produces only transesterification.

Dow Chemical U.S.A, Experimental Ethylene Carbonate XAS-1666.00L Product Bulletin (1982), p. 12, describes the preparation of ethylene sulfide from the reaction of ethylene carbonate with potassium thiocyanate at a temperature of 100° C. It is stated that 2-oxazolidinones can be prepared from the reaction of aryl or alkyl isocyanates with ethylene carbonate in the presence of a catalyst. It is also stated that ethylene carbonate slowly decomposes to ethylene oxide in quantitative yields at a temperature above 200° C. and that this reaction is accelerated by the presence of catalysts such as inorganic and organic salts.

Texaco Chemical Company, TEXACAR® Ethylene and Propylene Carbonates Product Bulletin (1987), p. 24, discloses the reaction of ethylene carbonate with glycerine to give glycidol. It is stated that this reaction probably proceeds through the cyclic carbonate ester of glycerine. It is also stated that ethylene carbonate may be reacted with potassium thiocyanate at elevated temperature to give ethylene sulfide.

Carothers, W. H. et al., J. Am. Chem. Soc., 52, 1930, pp. 314-326, describes polymerization and ring formation of glycol esters of carbonic acid. Compounds prepared by the action of appropriate glycols on ethyl carbonate include trimethylene carbonate, tetramethylene carbonte, pentamethylene carbonate, hexamethylene carbonate, decamethylene carbonate, diethylene carbonate and p-xylylene carbonate.

DISCLOSURE OF THE INVENTION

This invention relates to a process for preparing cyclic ethers which comprises contacting a carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

This invention also relates to a process for preparing cyclic ethers which comprises contacting a polyhydroxyl-containing compound with a CO₂ synthon in the presence of a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

This invention further relates to a process for preparing cyclic ethers which comprises (i) contacting a polyhydroxyl-containing compound with a CO₂ synthon under conditions effective to produce a carboxylated ether, and (ii) contacting the carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

In a preferred embodiment, this invention relates to a process for preparing oxetane which comprises contacting trimethylene carbonate or poly(trimethylene carbonate) with a mixed metal oxide catalyst under conditions effective to produce oxetane.

The cyclic ethers produced in accordance with the processes of this invention include, for example, oxetane, alkylene oxides, glycidol, crown ethers, furans, pyrans, thiophenes, morpholine and the like, which are useful for a wide variety of applications such as solvents, liquid absorbents, chelating agents, phase transfer catalysts and the like.

For purposes of this invention, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 67th Ed., 1986-87, inside cover. Also, for purposes of this invention, Group IIIB metal oxides embraces the lanthanides and actinides. As used herein, the term "oxide" embraces oxides, hydroxides and/or mixtures thereof. Also, as used herein, the term "CO₂ synthon" embraces SO₂ synthons such as sulfurous acids and sulfurous acid esters. Sulfur analogs of cyclic ethers, i.e. cyclic thioethers, are also embraced by this invention.

DETAILED DESCRIPTION

As indicated above, this invention relates to a process for preparing cyclic ethers which comprises contacting a carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

As also indicated above, this invention relates to a process for preparing cyclic ethers which comprises contacting a polyhydroxyl-containing compound with a CO₂ synthon in the presence of a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

As further indicated above, this invention relates to a process for preparing cyclic ethers which comprises (i) contacting a polyhydroxyl-containing compound with a CO₂ synthon under conditions effective to produce a carboxylated ether, and (ii) contacting the carboxylated ether with a mixed metal oxide catalyst under conditions effective to produce the cyclic ether.

As yet further indicated above, in a preferred embodiment, this invention relates to a process for preparing oxetane which comprises contacting timethylene carbonate or poly(trimethylene carbonate) with a mixed metal oxide catalyst under conditions effective to produce oxetane.

When a polyhydroxyl-containing compound and CO₂ synthon are employed as starting materials, it is believed that a transesterification reaction followed by a decarboxylation reaction occurs to provide the desired cyclic ether product. The exact reaction mechanism is not fully appreciated but what is appreciated is that a polyhydroxyl-containing compound starting material and CO₂ synthon starting material can be contacted in the presence of a mixed metal oxide catalyst under conditions described herein to provide a cyclic ether product. It is also appreciated that a carboxylated ether can be contacted with a mixed metal oxide catalyst under conditions described herein to provide a cyclic ether product.

Step (i) of certain processes of this invention can in general be referred to as a transesterification reaction. Any suitable transesterification catalyst can be employed in step (i). Such transesterification catalysts are known and include, for example, basic metal oxides, alkoxides and other basic metal salts such as potassium carbonate, sodium titanate and the like. Other suitable transesterification catalysts include, for example, Bronsted acids such as sulfuric acid and Lewis acids such as aluminum triisopropoxide. As discussed hereinafter in regard to the decarboxylation catalyst, the transesterification catalyst employed in this invention likewise may also contain support(s), binding agent(s) or other additives to stabilize or otherwise help in the manufacture of the catalyst. Both homogeneous and heterogeneous catalysts can be employed in the step (i) reaction. The amount of transesterification catalyst used in step (i) is dependent on the particular catalyst employed and can range from about 0.01 weight percent or less to about 10 weight percent or greater of the total weight of the starting materials.

Suitable polyhydroxyl-containing compound starting materials which can be employed in the step (i) transesterification reaction include any permissible substituted or unsubstituted polyhydroxyl-containing organic compound(s) such as those embraced by the formula R(OH)_(m) wherein R is the residue of an organic compound and m is a value which satisfies the valencies of R, preferably m is a value of from 2 to about 6, more preferably m is a value of from 2 to about 4. Preferred polyhydroxyl-containing compound starting materials include substituted and unsubstituted dihydric and polyhydric alcohols.

Illustrative polyhydroxyl-containing compound starting materials useful in this invention include, for example, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, poly(oxyalkylene)glycols such as CARBOWAX® poly(oxyethylene)glycol materials, diethanolamine, triethanolamine, o-dihydroxybenzene and the like. Other suitable polyhydroxyl-containing compounds having 2 or more hydroxyl groups, e.g., about two to six hydroxyl groups and have 2 to 30 carbons, include glycerine, 1,3-propanediol, pentaerythritol, galactitol, sorbitol, mannitol, erythritol, trimethylolethane and trimethylolpropane. The molar ratio of polyhydroxyl-containing compound to CO₂ synthon is not narrowly critical and can range from about 0.05:1 or less to about 50:1 or greater, preferably from about 0.1:1 to about 10:1.

Suitable CO₂ synthon starting materials which can be employed in the step (i) transesterification reaction include any permissible substituted or unsubstituted carboxyl-containing compound(s) or carbonyl-containing compound(s) which are capable of reacting with a polyhydroxyl-containing compound under the process conditions described herein, such as those embraced by the formulae R₁ C(O)R₂ or R₁ S(O)R₂ wherein R₁ is hydrogen, halogen, amino, hydroxyl or the residue of an organic compound, and R₂ is amino, hydroxyl or the residue of an organic compound. Illustrative CO₂ synthons include, for example, substituted and unsubstituted carbonates, chlorocarbonates, carbonic acids, carbamates, carbamic acids, oxalates, 2-oxazolidinones, ureas, esters, phosgene, chloroformates, carbon dioxide, orthocarboxylates, sulfurous acids, sulfurous acid esters and the like. For purposes of this invention, carbon monoxide is also considered a CO₂ synthon for appropriate oxidative carbonylation reactions. Preferred CO₂ synthons include, for example, diphenyl carbonate, ethylene carbonate, dimethyl carbonate, 2-oxazolidinone, ethylene sulfite, phosgene and the like. The use of CO₂ synthons prepared in situ such as the reaction of ethylene carbonate and monoethanolamine to give 2-oxazolidinone is encompassed within the scope of this invention.

As indicated above, R₁ and R₂ can be the residue of an organic compound. Illustrative residues of organic compounds include, for example, alkyl, aryl, alkylamino, arylamino, cycloalkyl, heterocycloalkyl, alkyloxy, aryloxy, cycloalkyloxy, heterocycloalkyloxy, alkyloxycarbonyl, aryloxycarbonyl, cycloalkyloxycarbonyl, heterocycloalkyloxycarbonyl, hydroxycarbonyl and the like. Additionally, for purposes of defining the CO₂ synthon by the formulae above, the R₁ and R₂ substituents together can complete a cycloalkyl ring or a heterocycloalkyl ring which can be substituted or unsubstituted. The R₁ C(O)R₂ formula is also contemplated to embrace carbon dioxide and carbon monoxide.

The step (i) transesterification reaction can be conducted over a wide range of pressures ranging from atmospheric or subatmospheric pressures to superatmospheric pressures. However, the use of very high pressures has not been observed to confer any significant advantages but increases equipment costs. Further, it is preferable to conduct the step (i) reaction at reduced pressures of from about 1 mm Hg to less than about 760 mm Hg. The step (i) transesterification reaction is preferably effected in the liquid or vapor states or mixtures thereof.

The temperature of the step (i) transesterification reaction may be as low as about ambient temperature to about 300° C. Preferably, the reaction temperature ranges from about 50° C. to about 200° C., and most preferably from about 60° C. to about 120° C.

Suitable carboxylated ethers prepared by the step (i) transesterification reaction include any permissible substituted or unsubstituted carboxyl-containing ether compounds which are capable of eliminating carbon dioxide under the process conditions described herein, e.g., esters, carbonates, carbamates and the like, such as those embraced by the formulae ROC(O)OR₁, ROC(O)OR₂, ROC(O)OC(O)OR₁ or ROC(O)OC(O)OR₂ wherein R, R₁ and R₂ are as defined above. It is understood that the R and R₁ substituents together and the R and R₂ substituents together can complete a heterocycloalkyl ring which can be substituted or unsubstituted. Illustrative carboxylated ethers include, for example, trimethylene carbonate (1,3-propanediol carbonate), poly(trimethylene carbonate), 1,4-butanediol carbonate, ethylene glycol carbonate, diethylene glycol carbonate, triethylene glycol carbonate, tetraethylene glycol carbonate, pentaethylene glycol carbonate, hexaethylene glycol carbonate, poly(oxyalkylene)glycol carbonates such as CARBOWAX® poly(oxyethylene)glycol carbonate materials, glycerine carbonate, carboxylated crown ethers, carboxylated furans, carboxylated tetrahydrofuran, carboxylated pyrans and the like. Preferred carboxylated ethers are disclosed in Carothers, W. H. et al., supra, the disclosure of which is incorporated herein by reference. The amount of carboxylated ether(s) employed in step (ii) is dependent on the amount of mixed metal oxide catalyst employed.

The carboxylated ethers prepared by the step (i) transesterification reaction may undergo one or more transesterifications prior to the step (ii) decarboxylation reaction. For example, a hydroxyl-containing compound different from the polyhydroxyl-containing compound starting material may be reacted with the originally prepared carboxylated ether under conditions effective to prepare a different carboxylated ether. Suitable hydroxyl-containing compounds include those embraced by the formula R₃ OH wherein R₃ is the residue of an organic compound. This invention is not intended to be limited in any manner by the step (i) transesterification reaction.

Carboxylated ethers having a cyclic structure can be derived from any permissible polyhydroxyl-containing compound starting material and a CO₂ synthon starting material. Such compounds can be formed by an intramolecular or intermolecular condensation reaction. In some instances, carboxylated ethers having a cyclic structure can be generated from acyclic (poly)carbonates by an intramolecular nucleophilic attack at the carbonyl carbon followed by loss of an organic moiety. Also, in some instances, an intramolecular nucleophilic attack at the beta-carbon followed by loss of a CO₂ synthon, e.g., carbonate or carbamate, leads directly to the cyclic ether product.

Step (ii) of certain processes of this invention can in general be referred to as a decarboxylation reaction. Suitable decarboxylation catalysts which can be employed in step (ii) include two or more metal oxides. A magnesium:aluminum mixed metal oxide is a preferred mixed metal oxide catalyst as more fully described below. Both homogeneous and heterogeneous catalysts can be employed in the step (ii) reaction. The amount of decarboxylation catalyst used in step (ii) is not narrowly critical and is dependent on whether step (ii) is conducted batchwise or continuously. If batchwise, the catalyst employed can range from about 0.01 weight percent or less to about 10 weight percent or greater of the total weight of the starting materials. If continuously, generally a fixed bed is employed.

Suitable decarboxylation catalysts for use in the processes of this invention comprise mixed metal oxides containing two or more metal oxides. Illustrative of such mixed metal oxides include, for example, two or more of the following: Group IA metal oxides, Group IIA metal oxides, Group IIIB metal oxides (including lanthanides and actinides), Group IVB metal oxides, Group VB metal oxides, Group VIB metal oxides, Group VIIB metal oxides, Group VIII metal oxides, Group IB metal oxides, Group IIB metal oxides, Group IIIA metal oxides, Group IVA metal oxides, Group VA metal oxides or Group VIA metal oxides. Certain of these metal oxide(s) may also be used as transesterification catalysts in accordance with this invention such as Group IIA and/or IIIA metal oxides. Preferred mixed metal oxides are amphoteric or basic. Preferred mixed metal oxides which may be utilized as decarboxylation catalysts include, for example, two or more oxides of magnesium, aluminum, calcium, strontium, gallium, beryllium, barium, scandium, yttrium, lanthanum, cerium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium, ytterbium, niobium, tantalum, chromium, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, iron, cobalt, nickel, zinc, silver, cadmium, boron, indium, silicon, germanium, tin, lead, arsenic, antimony and bismuth.

Group IIA metal oxides such as magnesium oxide and calcium oxide and Group IIIA metal oxides such as aluminum oxide and gallium oxide are preferred mixed metal oxides for use in this invention. For mixed metal oxides in which at least one of the metals is magnesium, suitable metals in association with magnesium may include, for example, one or more of the following: Group IIIA metals such as boron, aluminum, gallium and indium, Group IIIB metals such as scandium, yttrium and lanthanum including the lanthanides, Group VB metals such as niobium and tantalum, Group VIB metals such as chromium, molybdenum and tungsten, Group VIII metals such as iron, cobalt and nickel, Group IIB metals such as zinc and cadmium, Group IVA metals such as silicon, germanium, tin and lead, Group VA metals such as arsenic, antimony and bismuth, and Group IVB metals such as zirconium and hafnium. For mixed metal oxides in which at least one of the metals is calcium, suitable metals in association with calcium may include, for example, one or more of the following: Group IIIA metals such as boron, aluminum, gallium and indium, Group IVA metals such as silicon, germanium, tin and lead, Group VB metals such as niobium and tantalum, and Group VIB metals such as chromium, molybdenum and tungsten.

Illustrative of mixed metal oxides which may be used as decarboxylation catalysts include, for example, MgO--Al₂ O₃, MgO--SiO₂, MgO--CdO, MgO--Bi₂ O₃, MgO--Sb₂ O₅, MgO--SnO₂, MgO--ZrO₂, MgO--BeO, MgO--TiO₂, MgO--CaO, MgO--SrO, MgO--ZnO, MgO--Ga₂ O₃, MgO--Y₂ O₃, MgO--La₂ O₃, MgO--MoO₃, MgO--Mn₂ O₃, MgO--Fe₂ O₃, MgO--Co₃ O₄, MgO--WO₃, MgO--V₂ O₅, MgO--Cr₂ O₃, MgO--ThO₂, MgO--Na₂ O, MgO--BaO, MgO--CaO, MgO--HfO₂, MgO--Li₂ O, MgO--Nb₂ O₅, MgO--Ta₂ O₅, MgO--Gd₂ O₃, MgO--Lu₂ O₃, MgO--Yb₂ O₃, MgO--CeO₂, MgO--Sc₂ O₃, MgO--PbO, MgO--NiO, MgO--CuO, MgO--CoO, MgO--B₂ O₃, CaO--SiO₂, CaO--Al₂ O₃, CaO--SnO, CaO--PbO, CaO--Nb₂ O₅, CaO--Ta₂ O₅, CaO--Cr₂ O₃, CaO--MoO₃, CaO--WO₃, CaO--TiO₂, CaO--HfO₂, MgO--SiO₂ --Al₂ O₃, MgO--SiO₂ --ZnO, MgO--SiO₂ --ZrO₂, MgO--SiO₂ --CuO, MgO--SiO₂ --CaO, MgO--SiO₂ --Fe₂ O₃, MgO--SiO₂ --B₂ O₃, MgO--SiO₂ --WO₃, MgO--SiO₂ --Na₂ O, MgO--SiO₂ --Ga₂ O₃, MgO--SiO₂ --La₂ O₃, MgO--SiO₂ --Nb₂ O₅, MgO--SiO₂ --Mn₂ O₃, MgO--SiO₂ --Co₃ O₄, MgO--SiO₂ --NiO, MgO--SiO₂ --PbO, MgO--SiO₂ --Bi₂ O₃, MgO--A1203--ZnO, MgO--Al₂ O₃ --ZrO₂, MgO--A1203--Fe₂ O₃, MgO--Al₂ O₃ --WO₃, MgO--Al₂ O₃ --La₂ O₃, MgO--Al₂ O₃ --Co₃ O₄, CaO--SiO₂ --Al₂ O₃, CaO--SiO₂ --SnO, CaO--SiO₂ --Nb₂ O₅, CaO--SiO₂ --WO₃, CaO--SiO₂ --TiO₂, CaO--SiO₂ --MoO₃, CaO--SiO₂ --HfO₂, CaO--SiO₂ --Ta₂ O₅, CaO--Al₂ O₃ --SiO₂, CaO--Al₂ O₃ --PbO, CaO--Al₂ O₃ --Nb₂ O₅, CaO--Al₂ O₃ --WO₃, CaO--Al₂ O₃ --TiO₂, the like. Other suitable mixed metal oxides embraced within the scope of this invention are disclosed by Tanabe et al., Bulletin of the Chemical Society of Japan, Vol. 47(5), pp. 1064-1066 (1974).

The mixed metal oxides described herein which can be used as decarboxylation catalysts may contribute to product selectivity and/or catalytic activity of the reaction and/or stability of the catalyst. As discussed hereinafter, the decarboxylation catalyst employed in this invention may also contain support(s), binding agent(s) or other additives to stabilize or otherwise help in the manufacture of the catalyst.

The decarboxylation catalysts which comprise two or more metal oxides may be prepared in a wide variety of ways. For example, the two or more metal oxides can be provided from metal salts which can either be heated or precipitated to form the mixed metal oxides. Also, two or more metal oxides may be provided as a partial condensate on a support, such as a silica or alpha, beta or gamma alumina, silicon carbide, and the like, and then condensed by heating to effect polymerization to the desired oxide form. The two or more metal oxides may be condensed from hydrolyzable monomers to the desired oxides, indeed, to form oxide powders which can thereafter be compressed in the presence of a condensation catalyst to form pellets and larger structures of the mixed metal oxide decarboxylation catalyst. A blend of the powders and condensation catalyst can be made into a shapeable paste which can be extruded and cut into pellets according to conventional procedures. The extrudate may thereafter be fired to cure the condensation catalyst and fix the structure. The cut extrudate may be blended with a support material such as those characterized above, and the blend fired to fuse the mixed metal oxide catalyst to the support.

In an embodiment of this invention, a magnesium salt, e.g., magnesium nitrate, and an aluminum salt, e.g., aluminum nitrate, are precipitated using ammonium hydroxide. The material is then washed with deionized water and calcined at a temperature of from about 350° C. to about 450° C. to afford the desired magnesium:aluminum mixed metal oxide catalyst.

In another embodiment, a magnesium oxide, e.g., magnesium carbonate hydroxide pentahydrate, and an aluminum oxide, e,g., aluminum hydroxide hydrate, are added to deionized water and thoroughly mixed to form a paste. The paste is then calcined at a temperature of from about 350° C. to about 450° C. to afford the desired magnesium:aluminum mixed metal oxide catalyst.

A typical catalyst structure comprises a Group IIA and IIIA mixed metal oxide having a surface area of at least about 100 m² /gm which may or may not be bonded to a support material. The decarboxylation catalysts on a support preferably have a surface area greater than about 20 m² /gm to as high as about 260 m² /gm, or greater depending upon which metal oxides are employed. In the case of magnesium:aluminum oxides, the surface area can be greater than about 50 m² /gm to as high as about 260 m² /gm, more preferably, greater than about 100 m² /gm to as high as about 260 m² /gm, determined according to the single point N₂ method.

The term "support," as used herein and in the claims, means a solid structure which does not adversely affect the catalytic properties of the catalyst and is at least as stable as the catalyst to the reaction medium. The support can function as a decarboxylation catalyst independent of the mixed metal oxide catalyst used herein, although it may have lower catalytic activity to the reaction. The support may act in concert with the catalyst to moderate the reaction. Some supports may contribute to the selectivity of the reaction. The catalyst structure can comprise from about 2 to about 60 percent by weight or greater of the support, more preferably from about 10 to about 50 percent by weight of the support, the remainder being the weight of the mixed metal oxides. Included in the weight of the support is the weight of any binding agent such as phosphates, sulfates, silicates, fluorides, and the like, and any other additive provided to stabilize or otherwise help in the manufacture of the catalyst. The support may be particles as large or larger than the catalyst component and "glued" to the decarboxylation catalyst by virtue of a binding medium.

The support may constitute a separate phase in the process of extruding the catalytic structure. In this embodiment, the support forming material, preferably as a paste is blended with a paste of the decarboxylation catalyst or a partial condensate thereof. The paste may comprise the oxide forms of the support and the decarboxylation catalyst, each blended with water, and/or binding agents. The extrudate of the blend is passed through a multiorificed die and chopped into pellets of the desired sizes. The particles may be doughnut shaped, spherical, and the like. Then the particles are calcined to dry them and complete any condensation reaction in the support and/or the mixed metal oxide decarboxylation catalyst.

A preferred group of mixed metal oxide catalysts for use in this invention include materials having the formula:

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (OH).sub.2x+3y-nz A.sub.z.sup.n-.aH.sub.2 O(I)

wherein M is at least one divalent metal cation; Q is at least one trivalent metal cation; and A is at least one anion providing a valence (n⁻), wherein n is at least 1, e.g., between 1 and 4 and most often between 1 and 3, and wherein a is a positive number, M, Q, and A are provided in a proportion such that x/y is a number equal to or greater than 1, z has a value greater than zero and 2x+3y-nz is a positive number. M, Q and A may be selected to provide a layered structure. Preferably, x/y is in the range of 1 to 12, more preferably x/y is in the range of 1 to 6 and most preferably is in the range of 1 to 4. Preferably, z has a value such that x/z is between n and 12n, more preferably between n and 6n and most preferably between n and 4n.

Suitable divalent metal cations, M, broadly include elements selected from the Transition elements and Groups IIA and IVA of the Periodic Table as well as certain Group IIIB elements. As specific examples can be mentioned magnesium, calcium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, palladium, platinum, copper, zinc, cadmium, mercury, tin and lead. Divalent metal cations which are particularly suitable are magnesium, nickel, cobalt, zinc, calcium, strontium and copper. Suitable trivalent metal cations, Q, broadly include elements selected from the Transition elements and Groups IIIA and VA of the Periodic Table as well as certain Group IIIB elements. As specific examples can be mentioned aluminum, antimony, titanium, scandium, bismuth, vanadium, yttrium, chromium, iron, manganese, cobalt, ruthenium, nickel, gold, gallium, thallium, and cerium. Trivalent metal cations which are particularly suitable can be selected from aluminum, boron, gallium and lanthanum.

The composition of formula (I) also can include a wide range of anions, A. Any anion or combination of anions which can balance the charge of the cations can be used. Suitable anions include inter alia. halides (such as chloride, fluoride, bromide, and iodide), nitrite, nitrate, sulfite, sulfate, sulfonate, carbonate, chromate, cyanate, phosphite, phosphate, molybdocyanate, bicarbonate, hydroxide, arsenate, chlorate, ferrocyanide, borate, cyanide, cyanaurate, cyanaurite, ferricyanide, selenate, tellurate, bisulfate, as well as organic anions such as oxalate, acetate, hexanoate, sebacate, formate, benzoate, malonate, lactate, oleate, salicylate, stearate, citrate, tartrate, maleate, and the like. The class of metalate anions described in U.S. Pat. No. 4,667,045, including metavanadate, orthovanadate, molybdate, tungstate, hydrogen pyrovanadate and pyrovanadate, also are suitable as anion A. Anions suitable for use in combination with the metal cations previously identified as being particularly suitable are carbonate, halide, phosphate, chromate, sulfate, hydroxide, oxalate, acetate, nitrate, hexanoate, sebacate, vanadate, molybdate, tungstate and ferrocyanate.

The foregoing lists of suitable divalent and trivalent cations and suitable anions are meant to be illustrative and not exclusive. Those skilled in the art will recognize that other cations and anions can be used provided that the specific type of cations and their relative amounts (x/y ratio) and the specific type of anions and their relative amount result in a mixed metal oxide composition.

Included in the materials identified above are those based on exchangeable anionic clay minerals. For example, compositions of formula (I) wherein M is magnesium and Q is aluminum are related to hydrotalcites, while compositions in which M is nickel and A is aluminum are related to takovites. In fact, mixed metal oxides prepared using magnesium, nickel or cobalt as the divalent cation and aluminum as the trivalent cation exhibit the typical X-ray diffraction pattern of a hydrotalcite.

In a more preferred aspect, the processes of this invention can utilize mixed metal oxide catalyst compositions prepared by calcining at an elevated temperature compositions according to formula (I). Suitable calcined compositions have the general formula:

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (O).sub.(2x+3y-nz)/w D.sub.z.sup.n-(II)

wherein M, Q, x, y, z and n have the same meanings defined above in connection with formula (I), and D is at least one nonvolatile anion. Nonvolatile anions may include, inter alia, halides, nitrates, phosphites, phosphate, vanadate, molybdate, tungstate, sulfite, sulfate, chromate, arsenate, borate, chlorate and the like. This list is illustrative and not exclusive.

Heat treating the formula (I) compositions to prepare the calcined mixed metal oxide compositions of formula (II) can be done, for example, at a temperature in the range of 200° C. to 800° C. for a period of time of about 12 to 24 hours under an inert atmosphere such as nitrogen or in appropriate cases under an oxidizing atmosphere such as air.

Calcination of the mixed metal oxide composition dehydrates the composition and converts at least partially the metal hydroxides to metal oxides. Any nonvolatile anions may be present in the calcined material.

Provided the calcination temperature is not excessive, the mixed metal oxide can be rehydrated to the mixed metal hydroxide with water. Generally, the mixed metal oxide can be restored readily if the calcination temperature does not exceed about 600° C. Mixed metal oxides which are calcined under more severe conditions are not easily rehydrated and lower surface area materials are obtained.

Certain compositions falling within formula (I), such as hydrotalcite, which comprises a magnesium-aluminum hydroxide carbonate, and takovite, which comprises a nickel-aluminum hydroxide carbonate, are naturally occurring compositions. However, such compounds, as well as their related compositions, also can be prepared synthetically from inexpensive starting materials using well-known coprecipitation techniques. Procedures for direct synthesis of such materials are described in Itaya et al., Inorg. Chem. (1987) 26:624-626; Taylor, R. M., Clay Minerals (1984) 19:591-603; Reichle, U.S. Pat. No. 4,476,324; Bish, D. L., Bull. Mineral (1980), 103:170-175 and Miyata et al., Clays and Clay Minerals (1977), 25:14-18. Using direct synthesis one has the ability to vary within wide limits the M⁺² /Q⁺³ atomic ratio as well as the anion.

For example, a composition of formula (I) where M⁺² is nickel or magnesium, Q⁺³ is aluminum and A^(n-) is carbonate can be prepared by adding, as aqueous solutions, (a) a mixture of nitrates, sulfates or chlorides of nickel or magnesium and aluminum in a desired atomic ratio of nickel or magnesium to aluminum, e.g. 6 atoms of nickel as nickel chloride to 2 atoms of aluminum as aluminum chloride, to (b) an aqueous solution of a stoichiometric amount of sodium hydroxide and a water soluble salt of the desired anion, e.g., sodium carbonate. The two solutions are mixed at a temperature of about 25° C. to 35° C. with vigorous stirring over a several-hour period to produce a slurry. The slurry then is heated for about 18 hours at a temperature within the range of about 50° C. to 200° C. (preferably between about 60° C. to 75° C.) in order to control crystallization and the ultimate particle size of the resulting crystals. After filtering, and thorough washing and drying, the solids are recovered, typically as a powder.

As noted above, this procedure can be adapted to a wide variety of cations, cation atomic ratios and anion substitutions. For example, water soluble salts of divalent magnesium, cobalt, zinc, copper, iron and calcium can be substituted for the nickel chloride illustrated above, while water soluble salts of trivalent gallium and lanthanum can replace the aluminum chloride. A wide variety of other combinations also will be apparent to those skilled in the art. Generally, the rate of metal ion addition to the aqueous caustic/anion solution is not critical and can be varied widely. For example, a preferred preparation method is described in Schaper, H. et al., Applied Catalysis, 54,1989, 79-90, the disclosure of which is incorporated herein by reference. The reaction temperature also is not critical, although the temperature during the reaction preferably is kept below about 100° C. An important feature of the procedure is the use of efficient agitation during the mixing procedure to avoid the formation of undesired by-products.

Loading of an anion A or D into the mixed metal oxide compositions is influenced by a variety of factors including (i) the amount of anion used in the preparation relative to the metal cations, (ii) the atomic ratio of the metal cations (x/y) in the preparation procedure, (iii) the size of the cations and anions and (iv) the preparation procedure. As used herein, "loading" is defined as the amount of available valences provided by a desired anion A or D expressed as a percentage of the total available valences for anion A or D. For example, carbonate loading in a hydrotalcite-type catalyst can be maximized by (i) using an excess (e.g., a greater than 3:1 molar ratio) of sodium carbonate to aluminum chloride during catalyst preparation and (2) adjusting the atomic ratio of magnesium to aluminum cations to about 2:1.

Mixed metal oxide compositions suitable as catalysts also can be prepared from the native or synthetic hydrotalcite-type compositions by ion exchange. For example, hydrotalcite can be treated at ambient conditions with 0.01N phosphoric acid for about 18 hours to replace the carbonate anion with phosphate anion. A halide analog of hydrotalcite prepared directly or by anion-exchange could be contacted with molybdic acid or a water soluble salt thereof, or with a water soluble salt of tungstic acid or vanadic acid in order to substitute the transition metal anion for the halide anion in the catalyst structure thereby to produce a mixed metal oxide composition of formula (I). Other ion exchanges will be apparent to those skilled in the art.

Calcined mixed metal oxide compositions may exhibit a higher level of selectivity/activity than uncalcined compositions. If a calcined mixed metal oxide catalyst composition experiences any decline in selectivity, it can be regenerated by a heat treatment in the presence of air to restore at least a portion of its initial level of selectivity/activity enhancement and reused. Conditions discussed above for calcining the hydrated mixed metal oxide compositions are suitable for regenerating compositions which have experienced a decline in activity.

Catalysts having the formulas (I) and (II) above wherein M is at least one of magnesium and calcium, Q is aluminum or gallium, A is at least one of carbonate, bicarbonate, phosphate, sulfate and nitrate, x/y is between 1 and 20, z has a value which satisfies the relationship: x/z is between n and 12n, and a is a positive number, are generally preferred for vapor phase decarboxylation due to their combination of activity (conversion of precursor) and selectivity. A preferred process involves a vapor phase process using mixed metal oxide catalyst wherein M²⁺ is magnesium, Q³⁺ is aluminum, A^(n-) is carbonate, x/y is about 1, and z is about 1.

A group of preferred mixed metal oxide catalyst compositions which can be employed in the processes of this invention is disclosed in copending U.S. Pat. application Ser. No. 125,134, filed Nov. 25, 1987, the disclosure of which is incorporated herein by reference.

The step (ii) decarboxylation reaction may be effected in the liquid or vapor or supercritical liquid states or mixtures thereof. In this context, the vapor phase reaction is intended to refer to the general vapor state of the starting materials. Though the step (ii) decarboxylation reaction conditions may range from subatmospheric or atmospheric to superatmospheric conditions, it is desirable to run the step (ii) reaction from about 1 mm Hg to about 5,000 mm Hg, preferably from about 100 mm Hg to about 2,500 mm Hg.

The temperature of the step (ii) decarboxylation reaction may be as low as about 150° C. to about 500° C. Preferably, the reaction temperature ranges from about 175° C. to about 375° C., and most preferably from about 225° C. to about 350° C.

Suitable carboxylated ethers for use in the step (ii) decarboxylation reaction can be prepared by the step (i) transesterification reaction or by other methods such as the carbonylation of hydroxyl-containing compounds with carbon monoxide and oxygen at elevated temperatures in the presence of certain copper salts. Such a carbonylation process can be an alternative to the step (i) transesterification reaction and is encompassed within the generic scope of this invention. It is also appreciated that two or more CO₂ synthons can be reacted under conditions effective to produce a carboxylated ether.

The step (ii) decarboxylation reaction can be conducted in the presence of an inert diluent which can be either a liquid or gas. When a liquid diluent is employed, it should preferably be a good solvent for the starting materials, inert under the reaction conditions, and of such a nature that separation from the cyclic ether product will not be difficult. For instance, the boiling points of the diluent and the cyclic ether product should differ by an adequate amount and there should be no tendency of the diluent to form an azeotrope with the desired cyclic ether product.

Examples of useful liquid diluents that meet the foregoing qualifications include benzene, toluene, xylene, ethylbenzene, anisole, heptane, octane, nonane, decane, dibutyl ether, and the like. Hydrocarbons are preferred.

Illustrative gaseous diluents include for example, nitrogen, methane, hydrogen, carbon monoxide or carbon dioxide. The gaseous diluent should of course be chosen so that it does not prevent the preparation of the desired products.

While the use of such diluents may be beneficial, the processes of this invention can be operated using pure starting material(s) as a liquid or gaseous feed. The degree of dilution of the starting materials with various diluents may vary considerably depending upon any process constraints restricting the use of the diluent. For example, in commercial production, the use of very large quantities of some gaseous diluents may be disadvantageous due to the cost of pumping large volumes of the gaseous diluent and increased difficulty in isolating the cyclic ether product, which increase the energy costs of the process. With liquid diluents, the use of very large quantities may be disadvantageous due to the energy cost associated with large recovery and recycle. If the processes of this invention are to be carried out using a gaseous diluent, in general it is recommended that the starting material(s) constitute from about 1 to about 95, and preferably about 5 to about 50, mole percent of the starting material/carrier feed. Increasing the dilution of the starting material with a gaseous diluent such as hydrogen may tend to increase the selectivity of the reaction to the particular products desired. The amount of liquid diluent can vary widely, for instance, from no diluent to about 90 weight percent or greater of the total weight of the starting materials.

For processes of this invention in which a carboxylated ether is contacted with a mixed metal oxide catalyst under conditions effective to produce a cyclic ether or a polyhydroxyl-containing compound

and a CO₂ synthon are contacted in the presence of a mixed metal oxide catalyst under conditions effective to produce a cyclic ether or other related processes described herein, it is understood that the process conditions described herein for the step (ii) decarboxylation reaction can desirably be employed for such processes.

The processes of this invention are useful for preparing substituted and unsubstituted cyclic ethers such as those embraced by the formulae ROR₁ or ROR₂ wherein R, R₁ and R₂ are as defined above. It is understood that the R and R₁ substituents are bridged together and the R and R₂ substituents are bridged together to complete a heterocycloalkyl ring which can be substituted or unsubstituted. Illustrative cyclic ethers prepared by the processes of this invention include, for example, oxetane, alkylene oxides such as ethylene oxide and propylene oxide, glycidol, dioxane, trioxane, crown ethers such as 18-crown-6, decalyl-15-crown-5 and dibenzo-18-crown-5, furans such as tetrahydrofuran, pyrans, thiophenes, morpholine and the like.

Illustrative of suitable cyclic ether compounds which can be prepared by the processes of this invention include those permissible cyclic ethers, including any permissible derivatives of described cyclic ether compounds, which are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, 1984, the pertinent portions of which are incorporated herein by reference. Suitable cyclic ethers which can be prepared by the processes of this invention include those permissible cyclic ethers, including any permissible derivatives of described cyclic ether compounds, which are described in Pedersen, C. J., J. Am. Chem. Soc., 92, 1970, pp. 391-394 and Pedersen, C. J., J. Am. Chem. Soc., 89, 1967, pp. 7017-7021, the disclosures of which are incorporated herein by reference.

The cyclic ether products produced by the processes of this invention can be separated by distillation. For example, a crude reaction product can be subjected to a distillation-separation at atmospheric or reduced pressure through a packed distillation column. Reactive distillation may be useful in conducting the step (i) transesterification reaction.

The processes of this invention may be carried out using, for example, a fixed bed reactor, a fluid bed reactor, or a slurry reactor. The optimum size and shape of the catalyst will depend on the type of reactor used. In general, for fluid bed reactors, a small, spherical catalyst particle is preferred for easy fluidization. With fixed bed reactors, larger catalyst particles are preferred so the back pressure within the reactor is kept reasonably low.

The processes of this invention can be conducted in a batch or continuous fashion, with recycle of unconsumed starting materials if required. The reaction can be conducted in a single reaction zone or in a plurality of reaction zones, in series or in parallel or it may be conducted batchwise or continuously in an elongated tubular zone or series of such zones. The materials of construction employed should be inert to the starting materials during the reaction and the fabrication of the equipment should be able to withstand the reaction temperatures and pressures. Means to introduce and/or adjust the quantity of starting materials or ingredients introduced batchwise or continuously into the reaction zone during the course of the reaction can be conveniently utilized in the processes especially to maintain the desired molar ratio of the starting materials. The reaction steps may be effected by the incremental addition of one of the starting materials to the other. Also, the reaction steps can be combined by the joint addition of the starting materials to the decarboxylation catalyst. When complete conversion is not desired or not obtainable, the starting materials can be separated from the cyclic ether product, for example by distillation, and the starting materials then recycled back into the reaction zone.

The processes are conducted for a period of time sufficient to produce the cyclic ethers. The exact reaction time employed is dependent, in part, upon factors such as temperature, nature and proportion of starting materials, and the like. The reaction time will normally be within the range of from about one-half to about 100 hours or more, and Preferably from less than about one to about ten hours.

The processes may be conducted in either glass lined, stainless steel or similar type reaction equipment. The reaction zone may be fitted with one or more internal and/or external heat exchanger(s) in order to control undue temperature fluctuations, or to prevent any possible "runaway" reaction temperatures.

Illustrative of suitable reactants in effecting the processes of this invention include by way of example:

DPC--diphenyl carbonate

DMC--dimethyl carbonate

TMC--trimethylene carbonate

PH--phosgene

EC--ethylene carbonate

GLY--glycerine

GLYC--glycerine carbonate

PC--propylene carbonate

PG--1,3-propane diol

BG--1,4-butane diol

PTMC--poly(trimethylene carbonate)

DEA--diethanolamine

DEG--diethylene glycol

TEG--triethylene glycol

DHB--o-dihydroxybenzene

CCE--carboxylated crown ethers

CFU--carboxylated furans

CTHF--carboxylated tetrahydrofuran

CPY--carboxylated pyrans

Illustrative of suitable products prepared by the processes of this invention include by way of example:

OX--oxetane

GLC--glycidol

EO--ethylene oxide

PO--propylene oxide

CE--crown ethers

FU--furans

THF--tetrahydrofuran

PY--pyrans

DX--1,4-dixoane

MO--morpholine

CRN--18-crown-6

DBC--dibenzo-18-crown-5

Illustrative of permissible reactions encompassed within the scope of this invention include, for example, the following reactant/product combinations:

    ______________________________________                                         REACTANT(S)          PRODUCT(S)                                                ______________________________________                                         TMC                  OX                                                        EC                   EO                                                        PC                   PO                                                        DEG, DMC             DX                                                        GLY, EC              GLC                                                       GLYC                 GLC                                                       PG, DEC              OX                                                        BG, DEC              THF                                                       BG, DMC              THF                                                       BG, EC               THF                                                       PTMC                 OX                                                        DEA, DMC             MO                                                        DHB, DEG, DMC        DBC                                                       TEG, DPC             CRN                                                       CCE                  CE                                                        CFU                  FU                                                        CTHF                 THF                                                       CPY                  PY                                                        ______________________________________                                    

As used herein, the phrase "residue of an organic compound" is contemplated to include all permissible residues of organic compounds. In a broad aspect, the permissible residues include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic residues of organic compounds. Illustrative organic compound residues include, for example, alkyl, aryl, cycloalkyl, heterocycloalkyl, alkyl(oxyalkylene), aryl(oxyalkylene), cycloalkyl(oxyalkylene), heterocycloalkyl(oxyalkylene), hydroxy(alkyleneoxy) and the like. The permissible residues can be substituted or unsubstituted and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible residues of organic compounds.

As used herein, the term "substituted" is contemplated to include all permissible substituents of organic compounds. In a broad aspect, the permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, alkyl, alkyloxy, aryl, aryloxy, hydroxy, hydroxyalkyl, amino, aminoalkyl, halogen and the like in which the number of carbons can range from 1 to about 20 or more, preferably from 1 to about 12. The permissible substituents can be one or more and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible substituents of organic compounds.

Certain of the following examples are provided to further illustrate the processes of this invention.

EXAMPLE 1 Preparation of Decarboxylation Catalyst

A total of 44.1 grams of magnesium nitrate hexahydrate and 66.0 grams of aluminum nitrate nonahydrate were dissolved in 200 milliliters of distilled water to give a first solution. A total of 4.8 grams of ammonium carbonate was dissolved in 200 milliliters of concentrated ammonium hydroxide (28-29 weight percent) to give a second solution. About 100 milliliters of distilled water was heated in a flask at a temperature of 40° C. and the first and second solutions were combined simultaneously with good agitation using a mechanical stirrer. The rates of addition of the first and second solutions were adjusted to maintain a pH of 9-10. The total addition took 10 minutes and a final pH of 9.5 was obtained. The contents were stirred at a temperature of 40° C. for a period of 40 minutes. The resulting precipitate was filtered and washed (ca. 300 milliliters three to four times) with water at a temperature of 60° C. until the pH of the wash was neutral. The filter cake was dried at a temperature of 80° C. overnight. The weight of the dried filter cake was about 16 grams. The filter cake was then calcined in air at a temperature of 400° C. for a period of 3 hours to afford a magnesium:aluminum mixed metal oxide.

EXAMPLE 2 Preparation of Oxetane

Into a 10 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 2.16 grams of trimethylene carbonate and 0.257 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio of 3:1. The flask contents were heated to a temperature of 250° C. in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FlD) using a DB-1701 column. The collected products consisted of 0.825 grams (65 percent theoretical yield) of a 50/50 mixture of oxetane and allyl alcohol.

EXAMPLE 3 Preparation of Oxetane

Into a 10 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 2.06 grams of poly(trimethylene carbonate) and 0.255 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio of 3:1. The flask contents were heated to a temperature of 250° C. in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FlD) using a DB-1701 column. The collected products consisted of oxetane and allyl alcohol (0.76 ratio of oxetane/allyl alcohol).

EXAMPLE 4 Preparation of Oxetane

Into a 25 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 2.01 grams of poly(trimethylene carbonate), 0.51 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio of 3:1, and 10.03 grams of tetraglyme as a solvent. The flask contents were heated to a temperature of 250° C. in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FlD) using a DB-1701 column. The collected products consisted of oxetane and allyl alcohol (0.99 ratio of oxetane/allyl alcohol).

EXAMPLE 5-8 Preparation of Oxetane

Into a 25 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 1.0 gram of poly(trimethylene carbonate), 0.25 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio identified in Table A below, and optionally an amount of tetraglyme solvent identified in Table A. The flask contents were heated to a temperature of 250° C. in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FlD) using a DB-1701 column. The collected products consisted of oxetane and allyl alcohol. The oxetane/allyl alcohol ratios are set forth in Table A.

                  TABLE A                                                          ______________________________________                                         Example No.      5      6        7    8                                        ______________________________________                                         Tetraglyme, grams                                                                               0      10       0    10                                       Mg/Al ratio      2      2        5    5                                        Oxetane/Allyl Alcohol                                                                           1.23   1.52     0.50 0.64                                     ratio                                                                          ______________________________________                                    

EXAMPLES 9-12 Preparation of Oxetane

Into a 25 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 1.0 gram of trimethylene carbonate 0.25 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio identified in Table B below, and optionally an amount of tetraglyme solvent identified in Table B. The flask contents were heated to a temperature of 250° C. in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FID) using a DB-1701 column. The collected products consisted of oxetane and allyl alcohol. The oxetane/allyl alcohol ratios are set forth in Table B.

                  TABLE B                                                          ______________________________________                                         Example No.      9      10       11   12                                       ______________________________________                                         Tetraglyme, grams                                                                               0      10       0    10                                       Mg/Al ratio      2      2        5    5                                        Oxetane/Allyl Alcohol                                                                           1.08   1.11     0.49 0.61                                     ratio                                                                          ______________________________________                                    

EXAMPLES 13-15 Preparation of Oxetane

Into a 25 milliliter round bottom reaction flask equipped with a distillation column, thermometer and mechanical stirrer was added 1.0 gram of trimethylene carbonate (1,3-propane diol) and 0.25 grams of a magnesium:aluminum mixed metal oxide having a magnesium:aluminum ratio of 2:1. The flask contents were heated to a temperature identified in Table C below in an oil bath. The products distilled from the flask as they were formed and collected in a cold trap cooled to a temperature of -78° C. Analysis was performed by a capillary gas chromatograph (FlD) using a DB-1701 column. The collected products consisted of oxetane and allyl alcohol. The oxetane/allyl alcohol ratios are set forth in Table C.

                  TABLE C                                                          ______________________________________                                         Example No.     13         14      15                                          ______________________________________                                         Temperature °C.                                                                         225        250     275                                         Oxetane/Allyl Alcohol                                                                          0.60       1.08    1.08                                        ratio                                                                          ______________________________________                                    

Although the invention has been illustrated by certain of the preceding examples, it is not to be construed as being limited thereby; but rather, the invention encompasses the generic area as hereinbefore disclosed. Various modifications and embodiments can be made without departing from the spirit and scope thereof. 

We claim:
 1. A process for preparing oxetane which comprises contacting trimethylene carbonate or poly(trimethylene carbonate) with a mixed metal oxide catalyst under decarboxylation conditions effective to produce oxetane.
 2. A process for preparing oxetane and allyl alcohol which comprises contacting trimethylene carbonate or poly(trimethylene carbonate) with a mixed metal oxide catalyst under decarboxylation conditions effective to produce oxetane and allyl alcohol.
 3. The process of claim 1 wherein the mixed metal oxide catalyst comprises two or more Group IA metal oxides, Group IIA metal oxides, Group IIIB metal oxides, Group IVB metal oxides, Group VB metal oxides, Group VIB metal oxides, Group VIIB metal oxides, Group VIII metal oxides, Group IB metal oxides, Group IIB metal oxides, Group IIIA metal oxides, Group IVA metal oxides, Group VA metal oxides or Group VIA metal oxides.
 4. The process of claim 3 wherein the mixed metal oxide catalyst comprises two or more oxides of magnesium, aluminum, calcium, strontium, gallium, beryllium, barium, scandium, yttrium, lanthanum, cerium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, lutetium, ytterbium, niobium, tantalum, chromium, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, iron, cobalt, nickel, zinc, silver, cadmium, boron, indium, silicon, germanium, tin, lead, arsenic, antimony and bismuth.
 5. The process of claim 1 wherein the mixed metal oxide catalyst comprises at least one Group IIA metal oxide.
 6. The process of claim 1 wherein the mixed metal oxide catalyst comprises a Group IIA metal oxide and a Group IIIA metal oxide.
 7. The process of claim 1 wherein the mixed metal oxide catalyst comprises a Group IIA metal oxide and a Group IIIB metal oxide.
 8. The process of claim 1 wherein the mixed metal oxide catalyst comprises magnesium oxide and aluminum oxide.
 9. The process of claim 1 wherein the mixed metal oxide catalyst comprises a high surface area mixed metal oxide.
 10. The process of claim 1 wherein the mixed metal oxide catalyst has a surface area greater than about 50 m² /gm.
 11. The process of claim 5 wherein the Group IIA metal oxide comprises from about 10 weight percent to about 90 weight percent of the weight of the catalyst.
 12. The process of claim 1 wherein the mixed metal oxide catalyst is associated with a support material.
 13. The process of claim 12 wherein the support comprises an alumina material or an alumina-silica material.
 14. The process of claim 1 wherein the support comprises an silica material or a silica-alumina material.
 15. The process of claim 12 wherein the support comprises from about 2 to about 50 percent by weight of the mixed metal oxide catalyst.
 16. The process of claim 1 wherein the mixed metal oxide catalyst comprises:(a) a material having the formula:

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (OH).sub.2x+3y-nz A.sub.z.sup.n-31 .aH.sub.2 O(I)

wherein M is at least one divalent metal cation; Q is at least one trivalent metal cation; and A is at least one anion providing a valence (n⁻), wherein n is 1 to 4 and wherein a is a positive number, M, Q and A are provided in a proportion such that x/y is a number equal to or greater than 1, z has a value greater than zero and 2x+3y-nz is a positive number, or (b) a material prepared by calcining the material of formula (I) having the formula

    M.sub.x.sup.2+ Q.sub.y.sup.3+ (O).sub.(2x+3y-nz)/2 D.sub.z.sup.n-(II)

wherein M, Q, x, y, z and n have the same meanings defined above in connection with formula (I), and D is at least one nonvolatile anion.
 17. The process of claim 16 wherein x/y is a number between 1 and 12 and z has a value which satisfies the relationship: x/z is between n and 12n.
 18. The process of claim 16 wherein A is selected from the group consisting of carbonate, halide, phosphite, phosphate, chromate, sulfate, hydroxide, oxalate, acetate, nitrate, hexanoate, sebacate, vanadate, molybdate, tungstate and ferrocyanate.
 19. The process of claim 16 wherein D is selected from the group consisting of halides, phosphite, phosphate, vanadate, molybdate, tungstate, sulfite, sulfate, chromate, arsenate, borate and chlorate.
 20. The process of claim 16 wherein x/y is a number between 1 and 6 and z has a value which satisfies the relationship: x/z is between n and 6n.
 21. The process of claim 16 wherein said material prepared by calcining the material of formula (I) has been heat treated at a temperature in the range of 200° C. to 800° C. for 12 to 24 hours.
 22. The process of claim 16 wherein M is magnesium and Q is aluminum. 